zumdahl_chemprin_6e_csm_ch03

zumdahl_chemprin_6e_csm_ch03 - CHAPTER 3 STOICHIOMETRY...

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16 CHAPTER 3 STOICHIOMETRY Atomic Masses and the Mass Spectrometer 23. A = 0.0800(45.95269) + 0.0730(46.951764) + 0.7380(47.947947) + 0.0550(48.947841) + 0.0540(49.944792) = 47.88 amu This is element Ti (titanium). 24. Let x = % of 151 Eu and y = % of 153 Eu, then x + y = 100 and y = 100 x . 151.96 = 100 ) 9209 . 152 )( 100 ( ) 9196 . 150 ( x x + 15196 = (150.9196) x + 15292.09 (152.9209) x , 96 = (2.0013) x x = 48%; 48% 151 Eu and 100 48 = 52% 153 Eu 25. 186.207 = 0.6260(186.956) + 0.3740(A), 186.207 - 117.0 = 0.3740(A) A = 3740 . 0 2 . 69 = 185 amu (A = 184.95 amu without rounding to proper significant figures) 26. A = 0.0140(203.973) + 0.2410(205.9745) + 0.2210(206.9759) + 0.5240(207.9766) A = 2.86 + 49.64 + 45.74 + 109.0 = 207.2 amu; from the periodic table, the element is Pb. 27. There are three peaks in the mass spectrum, each 2 mass units apart. This is consistent with two isotopes, differing in mass by two mass units. The peak at 157.84 corresponds to a Br 2 molecule composed of two atoms of the lighter isotope. This isotope has mass equal to 157.84/2, or 78.92. This corresponds to 79 Br. The second isotope is 81 Br with mass equal to 161.84/2 = 80.92. The peaks in the mass spectrum correspond to 79 Br 2 , 79 Br 81 Br, and 81 Br 2 in order of increasing mass. The intensities of the highest and lowest masses tell us the two isotopes are present at about equal abundance. The actual abundance is 50.68% 79 Br and 49.32% 81 Br.
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C H A P T E R 3 S T O I C H I O M E T R Y 1 7 2 8 . S c a l e d I n t e n s i t y Compound Mass Intensity Largest Peak = 100 __________________________________________________________________ H 2 120 Te 121.92 0.09 0.3 H 2 122 Te 123.92 2.46 7.1 H 2 123 Te 124.92 0.87 2.5 H 2 124 Te 125.92 4.61 13.4 H 2 125 Te 126.92 6.99 20.3 H 2 126 Te 127.92 18.71 54.3 H 2 128 Te 129.92 31.79 92.2 H 2 130 Te 131.93 34.48 100.0 29. GaAs can be either 69 GaAs or 71 GaAs. The mass spectrum for GaAs will have two peaks at 144 (= 69 + 75) and 146 (= 71 + 75) with intensities in the ratio of 60 : 40 or 3 : 2. Ga 2 As 2 can be 69 Ga 2 As 2 , 69 Ga 71 GaAs 2 , or 71 Ga
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18 CHAPTER 3 STOICHIOMETRY 69 Ga (0.60) 71 Ga (0.40) 69 Ga (0.60) 0.36 0.24 71 Ga (0.40) 0.24 0.16 288 290 292 Moles and Molar Masses 30. 4.24 g C 6 H 6 × g 11 . 78 mol 1 = 5.43 × 2 10 mol C 6 H 6 5.43 × 2 10 mol C 6 H 6 × mol molecules 10 022 . 6 23 × = 3.27 × 10 22 molecules C 6 H 6 Each molecule of C 6 H 6 contains 6 atoms C + 6 atoms H = 12 total atoms. 3.27 × 10
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zumdahl_chemprin_6e_csm_ch03 - CHAPTER 3 STOICHIOMETRY...

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